The packaging of packs and packaged goods often involves films that are shrunk onto the wrapped products by means of heat treatment. Mostly so-called shrink tunnels are used for the heat treatment, in which the shrinking is achieved by means of a stream of hot air or hot gas—also called shrinking gas stream. The shrinking gas stream is generally applied to the side of the packaged units already wrapped with the shrink film in order to shrink the shrink film onto the packaged units and/or packs. In addition, the shrinking gas stream is also directed onto the bottom side of the product wrapped with the shrink film in order to seal, i.e. to melt together or fuse, the overlapping ends of the shrink film located there.
Such devices for generating hot gas for shrinking plastic films are known, for example, from DE 31 18 396 A1 and DE 38 26 358 A1.
The shrinking gas stream is provided by a hot gas or shrinking gas heater, which comprises at least one heating means operated, for example, by electricity or a gaseous or liquid fuel. A corresponding burner unit comprising a porous element with a gas stream passing therethrough for burning fuel gas and for generating heat is disclosed in DE 10 2007 030 264 A1. The heated gas passing through the porous element is fed into process air forming the shrinking gas stream.
Furthermore, a burner for a gas/air mixture is known from DE 43 22 109 C2. Such hot gas generators are additionally disclosed in DE 10 2007 011 526 A1 and EP 0 282 849 A1.